Tsuyoshi Ogino

Crystallinity of In2O3(ZnO)5 films by epitaxial growth with a self-buffer-layer

Naturally modulated structures, films of In2O3(ZnO)5, were epitaxially grown by rf magnetron sputtering on (0001) sapphire substrates. The crystallographic and morphological features of the films were characterized by using x-ray-diffraction and electron-diffraction patterns. The deposition of strongly c axis orientated films of In2Zn5O8 was achieved by epitaxy with a self-buffer layer (SBL). A film of In2Zn5O8 of approximately 10 nm in thickness was initially deposited as the SBL. This initial film was annealed in situ for 10–15 min, after which the bulk of the film of In2Zn5O8 was grown. Finally, well-crystallized In2O3(ZnO)5 films were obtained by annealing the resultant film at 800 °C. The electrical properties of the synthesized film are discussed in relation to the mechanism by which the modulated In2O3(ZnO)5 structure is formed.

High-efficiency Doherty linear amplifier with backoff control for mobile communications

This paper proposes a backoff control method for the Doherty amplifier that realizes both high efficiency and high linearity by using digital signal processing, which adapts to various modulation schemes in wireless communications. In order to achieve high efficiency, the control unit adjusts dc voltage of the carrier amplifier in the proposed Doherty amplifier linearized by input allocation for each branch. And the proposed amplifier has high efficiency and sufficient linearity for the signal with various peak-to-average power ratios from the different modulation schemes.

Low-Loss Transmission Characteristics of Transparent Conductive Thin Films in GHz Range

The resistivity of transparent conductive thin film formed by sputtering exhibits a dependence on film thickness. In this study, an analysis by electromagnetic field simulation of resistance effect on the transmission characteristics was carried out. The overall resistance of the signal waveguide governs the transmission characteristics, and variation of the resistance at the interface between the substrate and the thin film has no significant effect. We evaluated a structure in which fine metal wiring that is not visible to the eye is placed on transparent conductors to reduce the resistance of the transmitting waveguide. Electromagnetic field simulations suggest that this structure improves the transmission characteristics while keeping high transparency.

Electric property of ZnO based transparent conductor films in GHz range

Newly developed transparent transmission line structures using ZnO film and fine metal wiring that is not visible by eye have been designed. In this paper, some electromagnetic field simulations suggest that the structure improves transmission characteristics while keeping high transparency. It was revealed that the reflection characteristic of a new transparent coplanar waveguide (CPW) could be improved and the characteristic impedance was controlled well by the width of signal line of ZnO film.